The birds you see above are all ruffs (Philomachus pugnax): wading birds that summer in marshes through Northern Europe and Asia. All three are wearing different forms of breeding plumage. And all of them are male.
The differences in the way they look reflect differences in their strategies for finding mates. And a pair of studies in Nature Genetics this week show that those complex differences in plumage, body size, and behaviour are all controlled by one block of genes.
Ruffs are lekking birds: all the males gather in one area to strut their stuff for visiting females. Most males are large, grow a head tuft and a neck ruff of dark parti-coloured feathers, and defend a small dancing space on the lek where they try to attract females with an elaborate display of bowing, wing flipping, tail wriggling, and beating up other males.
White-ruffed satellite males are slightly smaller. They don't fight to keep a territory, but dance their displays on the edges of the lek and dash in to mate with females whenever the territorial males are distracted.
The rarest type of males are the faeders, which look exactly like the plain brown females. These males don't display at all — they sneak in and mate with females right under the beaks of the other males.
Two groups of geneticists, one led by Leif Andersson of Uppsala University, the other by Terry Burke of the University of Sheffield, have independently found that both the satellite males and the female-mimicking males share a chromosome containing a chunk of DNA that's flipped relative to what's found in the territorial males. The change is inherited as an unbroken stretch of DNA, so it can be considered a "supergene" that produces alternative male breeding strategies.
Andersson's team estimates that the flip happened about 3.8 million years ago. Since then, the 100-odd genes inside the flipped chunk of DNA have been collecting mutations, because they can't line up with the versions on the other chromosome for repair. Both teams identified mutated versions of genes that make proteins involved in steroid metabolism and feather pigmentation within the "supergene," which may be responsible for the differences in behaviour and appearance within satellite and faeder males. [Lamichhaney et al. 2015 [Küpper et al. 2015]] Top image by Susan McRae | Video by Jos Vroegrijk